WASHINGTON (CNN) -- The 2008 presidential campaign and the debate over the U.S. role in Iraq came together Tuesday as five White House hopefuls got a chance to question the Bush administration's top officials in the war effort.

The five senators running for president -- four Democrats and a Republican -- are in the position of trying to navigate the politics surrounding the Iraq war while they query Gen. David Petraeus and U.S. Ambassador to Iraq Ryan Crocker on whether the war in Iraq is worth the loss of more American lives.

Democratic candidates also had to make the tricky political calculations of how far to criticize Petraeus -- the public face of the administration's policies -- after an attack on his credibility by left-leaning MoveOn.org.

Before the end of the hearings, four Democratic presidential candidates who have called for the start of a troop withdrawal from Iraq -- Sens. Joe Biden, Chris Dodd, Hillary Clinton and Barack Obama -- had a chance to offer their comments and question Petraeus and Crocker.

New York's Clinton said she gave both men tremendous credit for presenting a positive view of a "rather grim reality" in Iraq, adding she believed they were dealt a very hard hand that was very unlikely to improve.

She then pressed Petraeus for a more specific response to a question posed by another senator earlier in the session: What if there's been very little progress in Iraq in a year from now? Watch candidates make their points »

"General, don't you think the American people deserve a very specific answer about what is expected from our country in the face of the failure of the Iraqi government to pursue its own required political agenda that they have essentially been unwilling or incapable of doing?" Clinton asked.

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"I will stand by the answer that I gave earlier, which is that I would be very hard pressed at that time to recommend a continuation," Petraeus replied.

The Iraq war is deeply unpopular among the American public. In a CNN/Opinion Research poll released Monday, 63 percent of those surveyed now oppose the war, with 34 percent supporting it. The poll's margin of error was plus or minus 3 percentage points.

And the war is even more unpopular among Democratic primary voters, something senators were constantly reminded of by the periodic disruptions of the hearings by anti-war protestors, and all of the Democratic presidential candidates have fought to position themselves as the candidate who can bring the troops home.

In contrast to the Democrats, Sen. John McCain, the one Republican presidential hopeful among the five, used the hearings to highlight the consequences of pulling troops out of Iraq.

"There is in some corners a belief that we can simply turn the page in Iraq, come home, and move on to other things," McCain said in his opening statement. "This is dangerously wrong. If we surrender in Iraq, we will be back -- in Iraq and elsewhere -- in many more desperate fights to protect our security and at an even greater cost in American lives and treasure."

Obama, who sits on the Foreign Relations Committee, faulted the timing of the hearings, saying that holding them on the sixth anniversary of the September 11, 2001, terrorists attacks reinforces the idea, mistaken in his view, that the Iraq war was tied to the overall fight against terrorism.

"I think we should not have had this discussion on 9/11 -- Or 9/10 or 9/12 -- because I think it perpetuates the notion that the original decision to go into Iraq was directly related to the attacks on 9/11," he said.

Obama also called the war "a disastrous foreign policy mistake."

"And we are now confronted with the question: How do we clean up the mess and make the best out of a situation in which there are no good options, there are bad options and worse options?" he said.

Biden, who supports a decentralized federal government in Iraq based on ethnic identity, said he doesn't believe continuing the surge over the next six months will change such a "reality."

"The majority of senators believe the time is now to start drawing down U.S. forces, not just to pre-surge levels but beyond them, and to limit the mission of those remaining to fight al Qaeda, train Iraqis and help protect the borders," he said.

"The surge, for whatever tactical or temporary security gains it might achieve, is at the service of a fundamentally flawed strategy," Biden said, echoing a belief not uncommon among fellow Democrats.

Dodd, who also sits on the Foreign Relations Committee, also used his opening statement Tuesday to criticize the president's war policy.

"In the eight months since President Bush announced the surge, we have spent tens of billions of dollars, over 700 American servicemen and women have sacrificed their lives, and nearly 4,400 have been wounded -- all to provide breathing space for the Iraqi government to engage in political reconciliation," Dodd said.

"And what has the Iraqi government done with this breathing space? It failed to meet vital political benchmarks it set for itself."

Dodd's presidential campaign expects the war in Iraq to be a focal point for the Connecticut Democrat, not only on the campaign trail but also in the Senate, a Dodd policy aide told CNN.

On Monday, MoveOn.org ran a full-page ad in The New York Times with the title "General Petraeus or General Betray Us?" accusing Petraeus of "cooking the books for the White House" and manipulating data to support the administration's policy.

During the hearings Tuesday, Republican senators decried the attack on Petraeus' character and pressed their Democratic colleagues to denounce it. On Monday, GOP presidential candidate Fred Thompson called on Democratic presidential candidates to return campaign contributions raised by the group.

A MoveOn.org spokesman told CNN that "no one has even talked to us" about returning the funds. MoveOn stands by the ad, the group says.

Possibly trying not to concede the political spotlight to his Senate competitors, Democratic presidential candidate Bill Richardson, governor of New Mexico, announced Tuesday he will lead "community discussions" about Iraq in Iowa this week.E-mail to a friend